Every diocese has an exorcist on staff. You can feel free to call your local diocese and ask for the exorcist’s office. You can explain the situation to him and then he can conduct an investigation to see if there is anything to your claim with regard to demonic possession. There is an excellent book that you can read called “The Rite” about an exorcist who gets trained in Rome and how he came to learn much about the process of exorcism.
With regards to your question though about people playing with witchcraft, etc…that indeed could have opened up the possibility of demonic entry–however it is fairly rare that a demon would stay around a house rather than stay with the people who were playing with the witchcraft. Ask the local exorcist for his opinion.
I would also say that while I don’t doubt the veracity of your claim, there are indeed a lot of crackpots who call the exorcist on a regular basis. So know that initially the exorcist will doubt your claim–and he should! The exorcist must always be doubtful before his investigation. So don’t be offended by this and rest easy if he doesn’t find anything. That should insure that your home indeed is not haunted.